Tandem Cells Research Articles

CuIn (Se,Te)2 Absorbers With Bandgaps <1 eV for Bottom Cells in Tandem Applications

ABSTRACTThin‐film solar cells reach high efficiencies and have a low carbon footprint in production. Tandem solar cells have the potential to significantly increase the efficiency of this technology, where the bottom‐cell is generally composed of a Cu(In,Ga)Se2 absorber layer with bandgaps around 1 eV or higher. Here, we investigate CuIn(Se1 − xTex)2 absorber layers and solar cells with bandgaps below 1 eV, which will bring the benefit of an additional degree of freedom for designing current‐matched two‐terminal tandem devices. We report that CuIn(Se1 − xTex)2 thin films can be grown single phase by co‐evaporation and that the bandgap can be reduced to the optimum range (0.92–0.95 eV) for a bottom cell. From photoluminescence spectroscopy, it is found that no additional non‐radiative losses are introduced to the absorber when adding Te. However, losses occur in the final solar cell due to non‐optimized interfaces. Nevertheless, a device with 9% power conversion efficiency is demonstrated with a bandgap of 0.97 eV and , the highest efficiency so far for chalcopyrites with band gap <1 eV. Interface recombination is identified as a major recombination channel for larger Te contents. Thus, further efficiency improvements can be expected with improved absorber/buffer interfaces.

Optimal performance of silicon nanowire solar cells under low sunlight concentration and their integration as bottom cells in III–V multijunction systems

Nanostructured silicon solar cells are designed to minimize costs through reduced material usage while enhancing power conversion efficiency via superior light trapping and shorter charge separation distances compared to traditional planar cells. This study identifies the optimal conditions for nanoimprinted silicon nanowire (SiNW) solar cells to achieve maximum efficiency under low sunlight concentration and evaluates their performance as bottom cells in III–V multijunction solar cell systems. The findings indicate that the SiNW solar cell reaches its peak performance at a concentration factor of 7.5 suns and a temperature of 40°C or lower. Specifically, the absolute conversion efficiency under these conditions is 1.05% higher than that under unconcentrated light. Compared to a planar silicon solar cell under identical conditions, the SiNW solar cell exhibits a 3.75% increase in conversion efficiency. Additionally, the SiNW single-junction solar cell, when integrated in series with a commercial lattice-matched InGaP/GaAs dual-junction solar cell, was tested under unconcentrated sunlight, specifically at one-sun, global air mass 1.5 condition, to assess its viability in one-sun multi-junction solar cell applications. The results suggest that a III–V upper subcell with a smaller active area than that of the SiNW subcell is optimal for maximizing current production, which is favorable to the cost reduction of the device. This hybrid configuration is particularly advantageous for terrestrial applications, such as electric vehicles, which demand lightweight, high-performance multijunction solar cell devices. Although the weight reduction of the characterized SiNW solar cell with a full silicon substrate compared to its planar solar cell counterpart is 1.8%, recommendations to increase this reduction to as much as 64.5% are discussed to conclude this paper.

Lead iodide secondary growth and π-π stack regulation for sequential perovskite solar cells with 23.62% efficiency

The sequential deposited perovskite solar cells (PSCs) have received widespread attention due to its application potential in large-scale perovskite module and perovskite/silicon tandem solar cells. However, insufficient reaction between organic ammonium salts and PbI2 leads to residual PbI2 and low crystallinity of perovskite films, and the fragile Pb-I bonds easily creates iodine loss and reduces the stability of PbI6 framework. In this work, the 4-fluorobenzylamine (FBA) with C = O and –NH2 is employed in PbI2 precursor solution to regulate the secondary growth process of PbI2 film. Due to the low Gibbs free energy and high crystallinity of porous PbI2 film, sufficient reaction between organic ammonium salts and PbI2 is promoted, which results in large-grain, low-defect perovskite films. At the same time, through hydrogen bonding and π-π stacking interactions, the stability of the PbI6 skeleton is effectively improved, significantly suppressing non-radiative recombination and reducing defect state density. Finally, this strategy increases the power conversion efficiency (PCE) of PSCs from 22.06 % to 23.62 %, and the target PSCs maintain 96 % of their initial PCE after being placed in nitrogen for 1300 h.

First-principles calculations to investigate Electronic, Optical, Mechanical, and transport characteristics of novel A2BAuCl6 (A = K/Rb/Cs; B = Sc/Y)

By utilizing FP-LAPW, the structure, electronic, optical, mechanical and Transport characteristic of A2BAuCl6 (A = K/Rb/Cs, B = Sc/Y) were examined by using DFT. The analysis to the band structure plot of the Halide double perovskites (HDP’s) being studied indicated the existence of indirect band-gaps. The compounds A2BAuCl6 (A = K/Rb/Cs, B = Sc/Y) exhibit anisotropic properties, except one compound as seen by their respective shear anisotropy readings of 0.629, 0.532, 1.006, 0.682, 0.803 and 0.977. The materials have inherent ductility, as indicated by their calculated Poisson’s ratios in the range of 0.30 to 0.35. The examined (HDP’s) materials appear to possess indirect band-gaps, as indicated by the band structure plots. The functional inorganic perovskites A2BAuCl6 (A = K/Rb/Cs, B = Sc/Y) haven’t similar band-gap values, as determined using the TB-mBJ (modified Becke Johnson) and TB-mBJ + Soc (Spin orbital coupling) assumptions. The visible and ultraviolet domain have prominent peaks, suggesting potential applications of the compounds in solar cells. Moreover, examination of additional optical characteristics such as reflectivity, conductivity, electron energy loss, and absorption coefficients suggest that it possesses the inherent features of a semiconductor. The maximum figure of merit for all the student compounds is above 0.74. The simulated output forms the foundation for A2BAuCl6 (A = K/Rb/Cs, B = Sc/Y) and are of practical importance for multijunction solar cells.

Influence of Composition on Mechanical Properties and Sound Speed of AlAs1−xPx for Various Pressures

The mechanical properties of AlAs1−xPx alloy under the influence of composition have been determined. The sound speed of AlAs1−xPx has been determined at various compositions. The studied properties were obtained with the effect of composition at various pressures. The predicted values were consistent with the available experimental results. The investigation used empirical method calculations based on empirical pseudo potential theory (EPM) with the virtual crystal approximation (VCA) to broaden the applications of ternary alloys and better investigate their potential as novel materials. AlAs1−xPx is a material that shows promise for usage in multi-junction solar cell designs because its properties can potentially be adjusted. The mechanical stability of AlAs1−xPx alloys was obtained according to these conditions C11 + 2C12 > 0, C44 > 0, and C11-C12 > 0. The obtained anisotropy factor was not equal to 1, indicating the presence of elastic anisotropy in the studied alloy in the applied composition range. The AlAs1−xPx alloy is a ductile material throughout the entire composition range at various pressures due to the Bu/Cs values exceeding 1.75.

Defect passivation engineering for achieving 4.29% light utilization efficiency MA-free wide-bandgap semi-transparent perovskite solar cells

Wide-bandgap perovskite materials are a great candidate for semitransparent perovskite solar cells (ST-PSCs) due to their tunable bandgap, outstanding transparency, and excellent photovoltaic performance. Though Br-rich perovskite can widen the bandgap, Br influences the crystallization dynamic speed leaving small perovskite grain sizes and high defects. Surface passivation engineering has been one of the best choices to suppress defects caused by the rapid crystallization of Br-rich perovskites. Herein, we applied MA-free perovskite as a light absorber because of the erratic thermal aging of MA-containing perovskites and selected phenethylammonium iodide (PEAI) and 4-trifluoro phenylethylammonium iodide (CF3PEAI) as passivation materials for improving the performance of opaque PSCs and ST-PSCs. Consequently, CF3PEA possesses a larger dipole moment. It has been demonstrated to exhibit a stronger binding energy with the substrate than PEA by density functional theory (DFT) calculations. This enhanced molecular interaction underpins the performance improvements in our solar cells, which manifests as an inverted planar structure opaque PSCs with 1.78 eV bandgap achieve a power conversion efficiency (PCE) of 17.09 % with excellent stability. A PCE of 17.17 % with 25 % average visible-light transmittance (AVT) and 4.29 % light utilization efficiency (LUE) of ST-PSCs is achieved by further optimizing the fabrication process of the buffer layer for protecting the perovskites from the damage of ITO sputter. Meanwhile, a four-terminal tandem solar cell with ST-PSC and silicon-based passivated emitter rear cell (PERC) obtains a PCE of 26.28 %. This work provides a feasible way to fabricate high-performance ST-PSCs with limited materials and preparation conditions.

Highly passivated TOPCon bottom cells for perovskite/silicon tandem solar cells

Tunnel oxide passivated contact (TOPCon) silicon solar cells are rising as a competitive photovoltaic technology, seamlessly blending high efficiency with cost-effectiveness and mass production capabilities. However, the numerous defects from the fragile silicon oxide/c-Si interface and the low field-effect passivation due to the inadequate boron in-diffusion in p-type polycrystalline silicon (poly-Si) passivated contact reduce their open-circuit voltages (VOCs), impeding their widespread application in the promising perovskite/silicon tandem solar cells (TSCs) that hold a potential to break 30% module efficiency. To address this, we have developed a highly passivated p-type TOPCon structure by optimizing the oxidation conditions, boron in-diffusion, and aluminium oxide hydrogenation, thus pronouncedly improving the implied VOC (iVOC) of symmetric samples with p-type TOPCon structures on both sides to 715 mV and the VOC of completed double-sided TOPCon bottom cells to 710 mV. Consequently, integrating with perovskite top cells, our proof of concept of 1 cm2 n-i-p perovskite/silicon TSCs exhibit VOCs exceeding 1.9 V and a high efficiency of 28.20% (certified 27.3%), which paves a way for TOPCon cells in the commercialization of future tandems.

Multi-Junction Solar Module and Supercapacitor Self-Powering Miniaturized Environmental Wireless Sensor Nodes

A novel prototype based on the combination of a multi-junction, high-efficiency photovoltaic (PV) module and a supercapacitor (SC) able to self-power a wireless sensor node (WSN) for outdoor air quality monitoring has been developed and tested. A PV module with about an 8 cm2 active area made of eight GaAs-based triple-junction solar cells with a nominal 29% efficiency was assembled and characterized under terrestrial clear-sky conditions. Energy is stored in a 4000 F/4.2 V supercapacitor with high energy capacity and a virtually infinite lifetime (104 cycles). The node power consumption was tailored to the typical power consumption of miniaturized, low-consumption NDIR CO2 sensors relying on an LED as the IR source. The charge/discharge cycles of the supercapacitor connected to the triple-junction PV module were measured under illumination with a Sun Simulator device at selected radiation intensities and different node duty cycles. Tests of the miniaturized prototype in different illumination conditions outdoors were carried out. A model was developed from the test outcomes to predict the maximum number of sensor samplings and data transmissions tolerated by the node, thus optimizing the WSN operating conditions to ensure its self-powering for years of outdoor deployment. The results show the self-powering ability of the WSN node over different insolation periods throughout the year, demonstrating its operation for a virtually unlimited lifetime without the need for battery substitution.

Expanding the Notch Region by Adjusting the Copper Growth Profile for High-Efficiency Flexible Cu(In,Ga)Se2 Solar Cells.

Flexible CIGS solar cells, with their adjustable band gap for future flexible tandem solar cells and flexibility for roll-to-roll manufacturing, have the potential to be used in a wide range of applications. However, flexible CIGS solar cells are always manufactured at relatively low temperatures, where Cu diffusion has a substantial impact on the CIGS surface state and defect formation. To address these issues, we designed a new CIGS growth profile in this work by carefully examining the effects of different locations of excess Cu in the third stage of the CIGS deposition profile. The results showed that adding more Cu to the middle part of the third stage can enhance the crystal quality, expand the GGI grading notch region, move the GGI minimum to the CdS side, cause a JSC rise, achieve proper band alignment at the interface, and then enhance the FF. By taking advantage of these advantages, the photoelectric conversion efficiency (PCE) is significantly raised. An impressive improvement of 32.6% over the initial efficiency of 13.8% has been attained, yielding a high efficiency of 18.3% and providing a strong basis for the development of flexible CIGS solar cells.

A Broadband Light‐Trapping Nanostructure for InGaP/GaAs Dual‐Junction Solar Cells Using Nanosphere Lithography‐Assisted Chemical Etching

III–V‐based multijunction solar cells have become the leading power generation technology for space applications due to their high power conversion efficiency and reliable performance in extraterrestrial environments. Thinning down the absorber layers of multijunction solar cells can considerably reduce the production cost and improve their radiation hardness. Recent advances in ultrathin GaAs single‐junction solar cells suggest the development of light‐trapping nanostructures to increase light absorption in optically thin layers within III–V‐based multijunction solar cells. Herein, a novel and highly scalable nanosphere lithography‐assisted chemical etching method to fabricate light‐trapping nanostructures in InGaP/GaAs dual‐junction solar cells is studied. Numerical models show that integrating the nanostructured Al2O3/Ag rear mirror significantly enhances the broadband absorption within the GaAs bottom cell. Results demonstrate that the light‐trapping nanostructures effectively increase the short‐circuit current density in GaAs bottom cells from 14.04 to 15.06 mA cm−2. The simulated nanostructured InGaP/GaAs dual‐junction structure shows improved current matching between the GaAs bottom cell and the InGaP top cell, resulting in 1.12x higher power conversion efficiency. These findings highlight the potential of light‐trapping nanostructures to improve the performance of III‐V‐based multijunction photovoltaic systems, particularly for high‐efficiency applications in space.

Multifunctional Ammonium Sulfide Enables Highest Efficiency Lead–Tin Perovskite Solar Cells

AbstractThe commonly used hole transport layer (HTL) Poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) still has some shortcomings that will limit the development of Pb–Sn perovskite solar cells (PSCs). In this work, multifunctional ammonium sulfide (AS) is attempted to modify PEDOT:PSS/perovskite interface. AS has multiple effects on different functional layers and the device as a whole: a) optimize the perovskite crystallization by the formation of PbS nucleation sites; b) neutralize the acidity of PEDOT:PSS by reaction with PSS; c) promote carrier transport at HTL/perovskite interface by tuning the energy level of PEDOT:PSS. As a result, a power conversion efficiency of 24.23% is obtained in the reverse scanning direction and 23.84% in the steady‐state output power test for the single‐junction Pb–Sn PSCs, and 27.48% for all‐perovskite tandem solar cells. These results show that AS modification can be an effective way to boost the development of Pb–Sn PSCs.

The Sustainable Development Trend, Progress and Challenge of Solar Cells

The current development of solar cells indicates that this field is experiencing rapid technological progress and market expansion. Various types of solar cells, from traditional silicon-based ones to emerging thin-film, dye-sensitized, perovskite, and organic solar cells, are constantly being developed to improve efficiency, reduce costs, and meet different application needs. While silicon-based solar cells remain one of the most mainstream types on the market, researchers are exploring third-generation photovoltaic devices such as multi-junction series cells, intermediate band gap cells, multiple exciton-generating cells hot carrier cells thermal-light photovoltaic solar cells to further bolster efficiency and reduce costs. These new solar cell technologies theoretically offer higher conversion efficiency and are anticipated to replace traditional silicon-based ones in the future. Advancements in the technology of solar cells mainly involve continuous progress and innovation in materials' development structural design manufacturing processes-from early silicon-based designs to today's thin-film arrays. Each generation is developed with the goal improving efficiency lowering costs; subsequently leading to recent developments in organic and perovskite arrays currently under exploration creating a final product at a lower price. At present, current attention within development primarily lies towards material components advancement efficiency maximization. Cost reduction strategies large scale production Although faced with certain obstacles; through consistent research proving their overwhelming effectiveness; implications for widespread use suggest performance. Overall prospects within Solar energy appear limitless.

Advancements of highly efficient perovskite based tandem solar cells

Advancements of highly efficient perovskite based tandem solar cells

Development of Novel Ternary Alloy of CSiSn for Low-Cost Next Generation Photovoltaics

The growing need for highly efficient solar cells calls for significant advancements in the development of a new material system to meet the needs of low-cost and low-cost production. Current multi-junction solar cell alternatives are more costly to produce. This research showcases the development and analysis of a novel ternary material system, The CSiSn (CST) alloy, which shows potential for creating low-cost material with high absorption in of solar spectrum. In this work, the following aspects regarding the CST material are investigated: 1) Material modeling using density functional theory, 2) electronic band structure estimations, 3) low-temperature material growth technique via Plasma Enhanced Chemical Vapor Deposition (PE-CVD) system; 4) advanced material and optical characterizations of CST alloys.

Performance evaluation of two-terminal tandem solar cells using cesium-based lead-free double perovskite top-cell for higher efficiency and better stability

Performance evaluation of two-terminal tandem solar cells using cesium-based lead-free double perovskite top-cell for higher efficiency and better stability

Bandgap Engineering via Doping Strategies for Narrowing the Bandgap below 1.2 eV in Sn/Pb Binary Perovskites: Unveiling the Role of Bi3+ Incorporation on Different A-Site Compositions.

The integration of perovskite materials in solar cells has garnered significant attention due to their exceptional photovoltaic properties. However, achieving a bandgap energy below 1.2 eV remains challenging, particularly for applications requiring infrared absorption, such as sub-cells in tandem solar cells and single-junction perovskite solar cells. In this study, we employed a doping strategy to engineer the bandgap and observed that the doping effects varied depending on the A-site cation. Specifically, we investigated the impact of bismuth (Bi3+) incorporation into perovskites with different A-site cations, such as cesium (Cs) and methylammonium (MA). Remarkably, Bi3+ doping in MA-based tin-lead perovskites enabled the fabrication of ultra-narrow bandgap films (~1 eV). Comprehensive characterization, including structural, optical, and electronic analyses, was conducted to elucidate the effects of Bi doping. Notably, 8% Bi-doped Sn-Pb perovskites demonstrated infrared absorption extending up to 1360 nm, an unprecedented range for ABX3-type single halide perovskites. This work provides valuable insights into further narrowing the bandgap of halide perovskite materials, which is essential for their effective use in multi-junction tandem solar cell architectures.

Progress of Hole-Transport Layers in Mixed Sn-Pb Perovskite Solar Cells.

Hybrid organic-inorganic lead halide perovskite solar cells (PSCs) have rapidly emerged as a promising photovoltaic technology, with record efficiencies surpassing 26%, approaching the theoretical Shockley-Queisser limit. The advent of all-perovskite tandem solar cells (APTSCs), integrating Pb-based wide-bandgap (WBG) with mixed Sn-Pb narrow-bandgap (NBG) perovskites, presents a compelling pathway to surpass this limit. Despite recent innovations in hole transport layers (HTLs) that have significantly improved the efficiency and stability of lead-based PSCs, an effective HTL tailored for Sn-Pb NBG PSCs remains an unmet need. This review highlights the essential role of HTLs in enhancing the performance of Sn-Pb PSCs, focusing on their ability to mitigate non-radiative recombination and optimize the buried interface, thereby improving film quality. The distinct attributes of Sn-Pb perovskites, such as their lower energy levels and accelerated crystallization rates, necessitate HTLs with specialized properties. In this study, the latest advancements in HTLs are systematically examined for Sn-Pb PSCs, encompassing organic, self-assembled monolayer (SAM), inorganic materials, and HTL-free designs. The review critically assesses the inherent limitations of each HTL category, and finally proposes strategies to surmount these obstacles to reach higher device performance.

Effectiveness of 2-Terminal Perovskite/Perovskite/c-Si Triple-Junction Solar Cells: An Integrated Study with an Emphasis on Methylammonium Bismuth Iodide.

The growing interest in high-efficiency solar energy technologies has driven research on multijunction solar cells to flourish over the last several years. This study sheds light on the optical, structural, and morphological aspects of the (CH3NH3)3Bi2I9 ((MA)3Bi2I9) film by fabricating and analyzing it experimentally. This thorough investigation lays the groundwork for more research into the film's possible uses in solar cell technology. We performed simulations to enhance the efficiency of two-terminal (2T) perovskite/perovskite double junction and perovskite/perovskite/c-Si triple-junction solar cells (TJSC) by using the MA3Bi2I9 material. The power conversion efficiency was greatly increased by using 2T triple-junction solar cells; the increase was around 116.59% from single junction (13.80-29.89%) and 31.91% from double junction (22.66-29.89%). As far as we know, this is the first investigation of the efficacy of MA3Bi2I9 as a top layer in multijunction tandem configurations. This revolutionary approach allows both academics and industry experts to produce cost-effective and efficient tandem solar cells, thereby enhancing earth-based solar energy development.

Optical Simulations of Nanotextured All‐Perovskite Tandem Solar Cells

AbstractThis numerical study investigates, how textures at various locations of all‐perovskite tandem solar cells affect their optical performance. For this, hexagonal sinusoidal textures with 750 nm period and aspect ratios (height‐to‐period) of 27% (moderate) and 54% (pronounced) are considered. The optical simulations are performed with the finite element method and an algorithm to correct for the thick glass superstrate. The complex refractive index data of the wide‐bandgap (WBG) and narrow‐bandgap (NBG) perovskites with spectroscopic ellipsometry is determined. Texturing between the glass superstrate and the WBG perovskite top cell has an antireflective effect across the whole wavelength region. In contrast, texturing between the WBG perovskite top cell and the NBG perovskite bottom cell has no additional effect for a moderate texture but leads to light trapping in the NBG perovskite for a pronounced texture. Moderate texturing between the NBG perovskite absorber and the metal back contact leads to light trapping in the NBG perovskite but also excites surface plasmons in the copper back contact. Dielectric interlayers between the NBG perovskite and the metal back contact can reduce the plasmonic absorption losses. Texturing potentially allows to increase the current‐matched short‐circuit current density beyond 17 mA .

Optimization of Charge Extraction and Interconnecting Layers for Highly Efficient Perovskite/Organic Tandem Solar Cells with High Fill Factor.

Perovskite/organic tandem solar cells (POTSCs) have garnered significant attention due to their potential for achieving high photovoltaic (PV) performance. However, the reported power conversion efficiencies (PCEs) and fill factors (FFs) are still subpar due to the challenges associated with charge extraction in the organic bulk-heterojunction (BHJ) and significant energy losses in the interconnecting layers (ICLs). Here, a quaternary organic BHJ blend is developed to enhance the charge extraction in the organic subcell, contributing to an increased FF of ≥78% under 1 sun illumination and even more under lower illumination intensities. Meanwhile, energy losses in the ICLs are reduced via the incorporation of a self-assembly monolayer (SAM), (4-(3,6-Dimethyl-9H-carbazol-9-yl)butyl)phosphonic acid (Me-4PACz), in organic BHJ to form a MoOx/SAM interface and the thorough control of the MoOx thickness to suppress parasitic absorption. The resultant POTSCs achieve a remarkable PCE of 25.56% (certified: 24.65%), with a record FF of 83.62%, which is among the highest PCEs of POTSCs and the highest FF of all types of perovskite-based tandem solar cells (TSCs) till now. This work proves the optimization of charge extraction and ICLs are effective strategies to promote the performance of POTSCs to surpass other solution-processed perovskite-based TSCs in the near future.